Mercury is the best planet, in my humble but well-researched opinion. Sure, it may be small, rocky, and lacking an atmosphere, but how it came to look the way it does absolutely baffles scientists. It might even have water and carbon hidden away from the beginning of the Solar System. Tonight, scientists from the European Space Agency and the Japan Aerospace Exploration Agency are launching a mission that could uncover some of the secrets of this mysterious rock.

BepiColombo is the European Space Agency’s first mission to Mercury, and perhaps a sequel to the very successful MESSENGER mission to the planet that ended in 2015. BepiColombo comprises two spacecraft, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO), each loaded with instruments that will measure the planet’s magnetic field, its chemical makeup, how it feels the Sun’s gravity, and more.

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“It has a fanstastic sequence of instruments on it,” Timothy Yeoman, professor at the University of Leicester in the United Kingdom, told Gizmodo. “There’s no compromise in the design of the mission.”

Mercury truly is mysterious. It’s extremely dense, with an enormous iron-filled core that takes up a much larger percentage of the overall planet than Earth’s core does. Does that mean Mercury formed somewhere else in the Solar System and migrated inward? Or was it once a much larger planet that lost some of its surface to some large impact? It’s unclear.

But there’s more—Mercury generates its own confusing magnetic field. It has a single enormous tectonic plate. Mercury also appears to be shrinking. Due to its lack of an atmosphere and pock-marked interior, there are icy spots where the surface has never seen the Sun, on which there appears to be liquid water ice. MESSENGER found evidence that the planet is covered in carbon. And the planet’s orbit, which changes its orientation quicker than once predicted, offered an early proof of Einstein’s theory of general relativity. These days, scientists use the planet to test the limits of that theory.

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BepiColombo’s scientists seek to dig into all of these points with 16 instruments divided between the two spacecraft. Along the way, it will even take some measurements of Venus’ atmosphere, internal structure, and interaction with the Sun.

BepiColombo will launch tonight at the earliest, using the gravity of Earth, Venus, and Mercury to assist its seven-year journey to the rocky planet. It will arrive at a high orbit around Mercury, where JAXA’s Mercury Magnetospheric Orbiter will assume its position. Then, the ESA’s Mercury Planetary Orbiter will assume a lower orbit, from which it will image Mercury’s surface.

The new probe improves on several aspects of its predecessor MESSENGER, Sean Solomon, director of Columbia’s Lamont-Doherty Earth Observatory and MESSENGER principal investigator, told Gizmodo. “With BepiColombo, there will be two spacecraft instead of one, they will be in orbits with approximately comparable coverage of the northern and southern hemispheres, and the two probes collectively carry many more instruments than MESSENGER.”

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Solomon explained that BepiColombo will greatly improve on maps of the planet’s surface composition, gravity field, topography, and polar deposits, especially in the southern hemisphere, which was harder to characterize with MESSENGER’s eccentric orbits. It will also better image the kinds of minerals on Mercury’s surface, and study certain aspects of the planet’s magnetic field with more authority because it will have two orbiters in different locations.

Like the Parker Solar Probe currently en route to the Sun, BepiColombo features newly developed insulation to protect itself from solar radiation. This insulation will play a role in the European Space Agency’s own upcoming Solar Orbiter.

I hope I’ve convinced you that BepiColombo is a mission worth getting excited about. After all, it will not only increase our understanding of Mercury; it could also reveal secrets of the history of the Solar System and enhance our understanding of gravity.

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You can watch the launch live below, starting at 9:15 pm US Eastern time, (3:15 am Central European Time).